1. Field of the Invention
The present invention relates to circuit breakers such as a molded-case circuit breaker or an earth leakage breaker, and more particularly to a circuit breaker in which contacts repel each other in order to open when a large current such as a short circuit is to be interrupted.
2. Description of the Related Art
FIG. 17 is a longitudinal cross-sectional view of one of three poles of a conventional circuit breaker. FIG. 18(A) is a top view of a second movable arm shown in FIG. 17 and FIG. 18(B) a side view thereof.
Referring to FIG. 17, a first movable arm 5 has a movable contact 5a and a second movable arm 4 has a fixed contact 4a. A housing 1 and a cover 2 are molded from resin. Within the housing 1, in addition to the first and second movable arms 4 and 5, are housed terminals 3 on the line side, arc suppressing chamber 6, switching gear 7, overcurrent tripping gear 8, and terminals 9 on the load side.
As shown in the figures, the second movable arm 4 is a generally V-shaped conductor and is rotatably supported at its bottom portion by means of a shaft 10 disposed on a support angle 11. The arm 4 is biased against the first movable arm 5 by a return spring 12 of a torsion coil type mounted on the shaft 10. The second movable arm 4 is connected to the terminal 3 via a lead 13 connected to a lower end of the arm 4.
The support angle 11 is made of pressed-steel. As shown in FIGS. 18(A) and 18(B), two opposing side walls 11b rise from a bottom 11a so that the overall shape of the angle 11 is a bifurcation. A stopper 11c rises from the bottom 11a to stop the second movable arm 4, which tends to rotate clockwise due to the urging force of the return spring 12. A U-shaped insulator 14 is inserted into the support angle 11 from right to left as shown in FIG. 18(B) so as to electrically isolate the support angle 11 from the lead 13. Then, as shown in FIG. 17, the insulator 14 and the support angle 11 are secured to the housing 1 by means of a bolt 15 inserted into a hole (not shown) in the bottom 11a of support angle 11. The terminal 3 is secured to the housing 1 by means of a bolt 17 inserted into a hole 16 as shown in FIG. 17.
FIG. 17 shows the circuit breaker when the contacts are closed. A current flows from the terminal 3 through lead 13, second movable arm 4, first movable contact 5a, lead 18, a heater and a lead 8b of overcurrent tripping gear 8 to the terminal 9. When a large current such as a short-circuit current flows through the circuit breaker, an electromagnetic repulsive force is developed between the arms 4 and 5 due to the fact that the current flowing in the arm 4 flows in a direction opposite to that in the arm 5, as depicted by arrows in FIG. 17.
The repulsive force drives the second arm 4 into counterclockwise rotation against the return spring 12 prior to contact-opening operation of the first arm 5. Then, the arc voltage across the contacts 4a and 5a is increased, and the switching gear 7, actuated by the overcurrent tripping gear 8, drives the first movable arm 5 to an open position to quickly perform a current-limiting circuit-breaking operation.
When assembling the aforementioned circuit breaker, the terminal 3 and the second movable arm 4 assembled together with the support angle 11 are placed in the housing 1 with the lead 13 connected between them. Since the lead 13 is a flexible wire having its two ends brazed into the arm 4 and terminal 3, respectively, the whole assembly is quite difficult to handle. In order to fix the assembly to the bottom of the housing 1 as shown in FIG. 17, it is required that the terminal 3 and the second movable arm 4 at each end of the lead 13, be positioned separately within the housing 1. Usually, repulsion type circuit breakers have deep housings as compared to non-repulsion types and it is therefore, time consuming to position the terminal and arm in such a deep housing.
In FIG. 17, the housing 1 is provided with a space 19 for each pole for accommodating a later described current-limiting resistor. The space 19 is closed by a rear cover 20. The rear cover 20 is glued to housing 1 by means of adhesive 21 as shown in FIG. 19, so that electrically conductive arc gas, typically produced when a large current such as a short-circuit current is interrupted, leaks between electrical conductors of each of three phases, or leaks from conductors inside the breaker to external conductors.
The adhesive 21 is a twin pack adhesive which is charged into a clearance between the housing 1 and the rear cover 20. This type of adhesive requires a long cure time. Furthermore, the amount and place of application of the adhesive tends to vary from worker to worker, resulting in inconsistent performance.